The invention concerns a device for a seismic streamer for use in the reception of reflection signals during seismic surveys at sea, where the streamer is towed behind a vessel and where the streamer is constructed with an external, tubular cover of a flexible plastic material.
When seismic surveys are conducted at sea, an array of normally parallel seismic energy sources, such as air guns are towed behind the vessel to transmit seismic signals which are reflected from the seabed, the reflected signals then being received by seismic detection cables, so-called streamers which contain hydrophones which record the signals and convey them back to the seismic vessel. These streamer cables will naturally be highly dependent on receiving signals which are really the reflected signals, and that these signals are the dominant signals received by the hydrophones. There are many problems which arise in this connection for a variety of reasons, some due to the cable itself and others to the environment. Objects in the water or in the surrounding area can cause a distortion of the signals received by the streamer cable's hydrophones. Some of the noise can also be generated by vibrations from the towing or from waves in the sea.
One of the problems which is particularly prevalent is that the streamer cable itself generates noise when it is towed through the water, this being due to the friction of the cable's skin or cover in the water. Many studies have been made of this type of noise from a vessel moving through the water, especially in connection with submarines which have to proceed as silently as possible, but in other contexts too, research has been carried out with regard to the surface of vessels with a view to reducing not only noise, but also surface friction. The most common theory has been that the surface should be made as smooth as possible in order to prevent friction, but theories have also been advanced that grooves should be made in the ship's surface in order to provide stability in the water and grooved surfaces have also proved to generate less noise.